[LLVMdev] Strong post-dominance in LLVM?

[Bjarke Roune]

On Thu, Jul 9, 2015 at 12:42 AM, James Molloy <james at jamesmolloy.co.uk>
 wrote:

> Forgive my naivety, but wouldn't that involve solving the halting problem?
>
> If I had to have the exact right answer for every input, then yes. If you
allow a return value of "I don't know" for some inputs, then you can solve
the halting problem trivially by always returning "I don't know". Better
solutions return "I don't know" on a smaller subset of the inputs. That the
halting problem is undecidable then just means that all correct solutions
must return "I don't know" for some inputs.

Bjarke

On Thu, Jul 9, 2015 at 12:42 AM, James Molloy <james at jamesmolloy.co.uk>
wrote:

> Hi Bjarke,
>
> Forgive my naivety, but wouldn't that involve solving the halting problem?
>
> Cheers,
>
> James
>
> On Thu, 9 Jul 2015 at 02:21 Bjarke Roune <broune at google.com> wrote:
>
>> There is PostDominatorTree for determining post-dominance. Even if A
>> post-dominates B and B is executed, that doesn't guarantee that A will be
>> executed. For example, there could be an infinite loop in-between. Strong
>> post-dominance makes the stronger guarantee that there will be no infinite
>> loop from B to A. Do we have anything in LLVM for determining strong
>> post-dominance and in general for guaranteeing that if B is executed, then
>> A will also be executed?
>>
>> Bjarke
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>
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